First, the yearly property tax question:
All boats are taxed at 10.5%. However, under Section 12-37-224, residents may be eligible for a 6% tax assessment if they meet all of the below criteria.
It is used as a second home
It has sleeping, bathroom and cooking facilities installed by the manufacturer
The interest portion of the indebtedness is deductible, or would be deductible if financed, pursuant to the Internal Revenue Code as an interest expense on a qualified primary or second residence
Next question was are there any good marina. I guess that depends on your definition of a "good marina". There are probably 15 in Charleston, several in Georgetown, 3 in Beaufort and a number in Hilton Head. You can go to their websites to get a sense of them or look at the reviews on Active Captain. As an example, Safe Harbor Charleston City Marina has 203 reviews and Charleston Harbor Marina has 174 reviews.